This invention relates to a gas turbine engine and, more particularly, to system for removing or separating foreign particles from the gaseous fluid flowing in the primary flow path of a gas turbine engine.
Gas turbine engines, particularly turboshaft gas turbine engines associated with helicopters, are susceptible to ingesting foreign particles. The tendency is associated with the variety of harsh environments in which the vehicle operates. Sand from deserts, salt from oceans and foliage from tropical environments are all potentially harmful to the engine and may deteriorate its performance.
The problems posed by ingestion of foreign particles into a gas turbine engine have been well known and attempts have been made previously to provide means for separating out foreign particles before the gaseous fluid, namely air, is supplied to the internal sections of the engine. One prior art approach which has proved to be particularly adept at this task is the particle separator and scroll scavenging means described in U.S. Pat. No. 3,832,086. The particle separator described in this patent imparts a radial velocity component to the particles in a direction away from the internal compressor air flow entrance. The particles are directed away from the compressor entrance and into a collection chamber. A blower is provided for establishing a vacuum which sucks the particles out of the collection chamber. This particle separation system has generally proved to be satisfactory in preventing damage to the internal engine components. However, the use of a blower to establish the vacuum for removing the particles from the collection chamber has added weight and cost to the system. Additionally, the blower must be periodically serviced, repaired and otherwise subjected to maintenance procedures which introduce additional expense in operating the engine.
Another prior art particle separator system, described by U.S. Pat. No. 3,766,719, provides suction for removing the particles from the separator collection chamber by permitting engine exhaust gases to flow past a nozzle connected by conduits to the collection chamber. A nozzle used in this manner is known as an ejector. The ejector depicted in this referenced patent discharges the stream of air in a direction generally parallel to the exhaust gases flowing in the main flow path. With parallel discharge, the ejector air stream and the exhaust gases are not immediately mixed and the exhaust duct of the engine must extend substantially downstream of the location at which the ejector is disposed to the exhaust gases in order to permit the two air streams to coalesce and generate a sufficient vacuum. With the ejector disposed downstream of the exit diffuser of the engine, the potential amount of generated vacuum is limited and the exhaust duct must be lengthened considerably in order to generate vacuum. Disposing the ejector upstream of the diffuser still requires the use of a duct extension ahead of the diffuser since the diffuser will not expand and decelerate the fluid stream unless the suction air is well coalesced with the mainstream gases. In either instance the use of an extended length of duct, to provide sufficient ejector suction, increases the cost, weight and length of the engine. Since the duct requires little or no servicing, this approach avoids the expenses related to maintaining a blower. However, the extra weight and costs associated with the extended duct are still undesirable characterics. Furthermore, the additional increases in overall length of the engine, due to the additional duct length, may itself make the engine unsuitable for vehicle applications having limited engine space requirements.